Referring to FIG. 10, as a refrigerant circuit 301 of an air conditioner of the above type, there is a known one which includes a main circuit 306 having a compressor 302, a condenser 303, a double-pipe type heat exchanger 310 for supercooling, a main expansion mechanism 304, an evaporator 305, a four-way changeover valve 309 and an accumulator 308 arranged in this order and a bypass circuit (indicated by dash lines) 313 which diverges from the main circuit 306 at a junction 321 between the condenser 303 and the double-pipe type heat exchanger 310, passes through a bypass expansion mechanism 312 and the double-pipe type heat exchanger 310 and joins the main circuit 306 at a juncture 322 in the vicinity of the inlet of the accumulator 308. A single refrigerant such as HCFC (hydrochlorofluorocarbon) 22 has conventionally been used as the refrigerant. The refrigerant discharged from the compressor 302 is condensed by the condenser 303 (which discharges heat to, for example, the outdoor air) and diverges at the junction 321 into a main-flow refrigerant which flows through the main circuit 306 and a bypass-flow refrigerant which flows through the bypass circuit 313. This main-flow refrigerant is supercooled by heat exchange with the bypass-flow refrigerant that has passed through the bypass expansion mechanism 312 in the double-pipe type heat exchanger 310 and thereafter reduced in pressure by the main expansion mechanism 304. Then, the main-flow refrigerant is evaporated by the evaporator 305 (which absorbs heat from, for example, the indoor air) and sucked into the compressor 302 through the four-way changeover valve 309 and the accumulator 308 for executing a gas-liquid separating operation. On the other hand, the bypass-flow refrigerant is reduced in pressure through the bypass expansion mechanism 312 and thereafter evaporated by heat exchange with the main-flow refrigerant in the double-pipe type heat exchanger 310. Subsequently, the bypass-flow refrigerant joins the main-flow refrigerant at the juncture 322 in the vicinity of the inlet of the accumulator 308.
By thus supercooling the main-flow refrigerant in the double-pipe type heat exchanger 310, a refrigerating effect to be produced by the main-flow refrigerant can be increased as compared with the case where no supercooling is executed. Furthermore, by diverging the bypass flow from the refrigerant flow, the volumetric flow rate of the main-flow refrigerant is reduced. Therefore, as indicated by a pressure to specific enthalpy diagram (referred to as a "Ph diagram" hereinafter) shown in FIG. 11B, a pressure loss .DELTA.P can be reduced inside the evaporator 305 and at the inlet side pipe of the compressor 302 (for the sake of comparison, a pressure loss .DELTA.P.sub.0 in the case where no supercooling is executed is shown in FIG. 11A). Accordingly, the refrigerating capacity of the system can be improved. It is to be noted that the portions denoted by A, B and C in FIG. 11B correspond to the states at the points A, B and C in the vicinity of the juncture 322 of the refrigerant circuit 301 shown in FIG. 10. As is clearly shown in FIG. 11C that is an enlarged view of part of FIG. 11B, the bypass-flow refrigerant reaching the point A and the main-flow refrigerant reaching the point B join together, thereby obtaining the state at the point C.
There is a constant demand for increasing the refrigerating capacity of the air conditioner, and there is no limitation on the demand for increasing the refrigerating capacity.